Multiple rotation gyroscope with hydrodynamic suspension

ABSTRACT

A gyroscopic device having an inertial element that is hydrodynamically suspended within a centralized cavity of a gimbal rotating simultaneously about two mutually perpendicular axes in which the moment of inertia and angular velocity about the first axis is greater than the moment of inertia and angular velocity about the second axis. Synchronously applied decentralizing forces acting on the inertial element are resisted by additional bearing surfaces that combine with the component of rotation having the smaller angular velocity to increase the restoring force on the inertial element in the direction of the decentralizing forces thereby maintaining the inertial element centered within the gimbal.

United States Patent [191 Passarelli, Jr.

[ MULTIPLE ROTATION GYROSCOPE WITH HYDRODYNAMIC SUSPENSION [75]Inventor: William O. Passarelli, J12, Jericho,

[73] Assignee: Sperry Rand Corporation, New

York, N.Y.

[22] Filed: Dec. 2, 1970 21] Appl. No.: 97,466

[52] US. Cl ..74/5, 74/5.7 [51] Int. Cl. ..G01c 19/16 [58] Field ofSearch ..l02/DIG. 3; 74/5, 5.42, -7

[56] References Cited UNITED STATES PATENTS 3,365,958 1/1968 Bard et al...74/5 3,048,043 8/1962 Slater et a1. ..74/5 3,522,737 8/1970 Brenot..74/5

Mar. 27, 1973 Primary Examiner-Robert F. Stahl Att0rneyS. C. Yeaton 57ABSCT A gyroscopic device having an inertial element that ishydrodynamically suspended within a centralized cavity of a gimbalrotating simultaneously about two mutually perpendicular axes in whichthe moment of inertia and angular velocity about the first axis isgreater than the moment of inertia and angular velocity about the secondaxis. synchronously applied decentralizing forces acting on the inertialelement are resisted by additional bearing surfaces that combine withthe component of rotation having the smaller angular velocity toincrease the restoring force on the inertial element in the direction ofthe decentralizing forces thereby maintaining the inertial elementcentered within the gimbal.

6 Claims, 5 Drawing Figures sa -Q PATfiNTt-jmmznms 3, 5

SHEET 10F 2 I/VVENTOR W/LL/AM O. PASSARELL/ JR A BY ATTORNEYPATENTEUHARZYISYS 3,7 2,295

SHEET 2 BF 2 INVENTOR VV/LL/AM O. PASS/JRELL/ JR.

A 7' TORNEY MULTIPLE ROTATION GYROSCOPE WITH HYDRODYNAMIC SUSPENSIONBACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention pertains to gyroscopic apparatus, particularly to suchapparatus havingan inertial element that is subjected to multiplerotation such No. 392,676 entitled, Multiple Rotation Gyroscope inventedby Albert D. Graefe, filed Aug. 25, l964 and assigned to the assignee ofthe present invention, and is hydrodynamically suspended in a fluidcontained within the gyroscope.

2. Description of the Prior Art Prior art inertial elements have beensupported by means of hydrostatic or hydrodynamic suspensions. However,auxiliary suspensions have been required during conditions of neutral ornegative buoyancy to maintain the inertial element centered within thegimbal or similar structure in which the inertial element may bedisposed. A number of techniques are available to provide thissupplementary support including capacitive, eddy current, hydrostaticand inductive suspensions. All of these suspensions require additionalcomponents, and power sources thereby limiting the minimum physical sizeof the gyro. Further, the extra components pose additional design andreliability problems For example, an auxiliary capacitive suspensionrequires capacitor plates, inductors, resistors, associated wiring,fluid region wire seals, a power supply, and a device such as a slipring or a rotary transformer for transmitting the necessary excitationto the gyros rotating structure. The instant invention requires noadditional components or power sources other than those already presentin the gyroscope.

SUMMARY OF THE INVENTION An inertial element (angular momentum element)subjected to rotation about two mutually perpendicular axes andsuspended in a relatively viscous fluid within a as described in thecopending U.S. Pat. application Ser. l

centralized cavity of a gimbal, rotates synchronously with the gimbalabout the first axis at a higher angular velocity than about the secondaxis. The multiple rotation of the inertial element provides essentiallytwo bearings each having a load carrying capacity. A primary bearing dueto rotation of the inertia] element about the fast spin axis produces astrong hydrodynamic centering force in the plane normal to the firstaxis, and a secondary bearing due to rotation about the slow spin axisproduces a smaller hydrodynamic centering force in the plane normal tothe second axis. Additionally, at temperatures below the neutralbuoyancy temperature, centrifugal forces cause centering of the inertialelement in the plane normal to the first axis. However, at neutralbuoyancy, these centrifugal forces cease to exist and since the inertialelement and rotor are rotating synchronously about the first axis, theprimary bearing has no load capacity for synchronous loads. Therefore,an auxiliary means is required to resist translation along the secondaxis due to synchronous loads applied parallel to the axis of smallerangular velocity. In the present invention, a third bearing is providedthrough the addition of bearing surfaces to either the inertial elementor the surface of the centralized cavity. These surfaces are comprisedof profiled grooves spiraling out from the region of the poles of theslow rotation axis. These added bearing surfaces utilize the rotation ofthe inertial element having the smaller angular velocity to provide asufficient restoring force to resist the decentering forces produced bythe synchronous loads applied parallel to the axis of slow rotation andmaintain the inertial element centered within the gimbal. Thiscompletely hydrodynamically suspended inertial element enablesconstruction of a smaller, less expensive and more efficient gyroscopicapparatus.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a cross-section diagram of ahydrodynamically suspended multiple rotation gyroscope. 5

FIGS. 2a and 2b are diagrams of the inertial element showing curvedgrooves on the surface of the element about the horizontal axis, B.

FIGS. 3a and 3b are isometric diagrams of the cavity showing curvedgrooves on the inner surface of the cavity about the horizontal axis, B.

DESCRIPTION OF THE PREFERRED EMBODIMENT The general operation of amultiple rotation gyroscope such as disclosed in the aforementionedcopending U.S. application Ser. No. 393,676 will be described withreference to FIG. 1 as embodied in a 2 of freedom gyroscope. Thegyroscope 10 has a case 11 within which a gimbal 12 is rotatablysupported to spin at a fast rotation speed (for example, 6,000 rpm)about a gimbal axis A. The gimbal 12 supports a spherical shapedinertial element 15 within a cavity 23 which-is spun at a slow rotationspeed'(for example, 60 rpm) with respect to the gimbal 12 about aninertial element axis Z which is almost perpendicular to the gimbal axisA. The inertial element 15 is also rotated in synchronism with thegimbal 12 about the inertial element axis V (at the high rotation speed)resulting in multiple rotation of the inertial element 15. The inertialelement rotation axes Z and V are slightly displaced from the verticalgimbal axis A and a horizontal gimbal axis B.

The inertial element 15 is constructed so that its moment of inertia,I,,, about the fast rotation axis, V, is greater than its moment ofinertia, 1,, about the slow rotation axis, Z. This is accomplished byhaving the major portion of the mass of the inertial element 15concentrated at the extremities of the inertial element axis, Z. Themultiple rotation of the inertial element 15 combines with the twodifferent moments of inertia, I,, and I,, with respect to the inertialelement axes, V and Z respectively, to produce highly stable operationand a reduction of the drift effects caused by any unbalances applied tothe inertial element 15. To illustrate this latter point, consider anunbalancing mass applied to a point on the spherical inertial element 15that is rotating about the two axes, V and Z, at two different rates.Since the point is moving with the inertial element 15, the point willtrace a helical-like path after a number of rotations about the fast andslow axes, V and Z. The time average position of the mass will be onlyslightly decentered from the support center of the spherical inertialelement 15, hence the resulting drift of the iner- 'tial element 15 willbe very small.

During steady state operating conditions of the inertial element willrotate at a slow angular velocity about the slow rotation axis, Z, andat a fast angular velocity about the fast rotation axis V. As shown inFIG. 1, the slow rotation axis Z is at an angle B slightly displacedfrom the horizontal axis B of the encompassing gimbal 12. The angle, Bbetween axis Z and axis B may be expressed as a'function of the angularvelocities and the moments of inertia of the inertial element 15, asfollows: 7

wherein Q angular velocity about the B axis 1,, moment of inertia aboutthe B axis (I angular velocity about the A axis 1 moment of inertiaabout the A axis Stable operation of the inertial element 15 requiresthat the angle B,, be minimized, and from the foregoing equation itfollows that the Sin 8,, must be kept small. As mentioned previously,the moment of inertia, I with respect to the fast rotation axis V ismade greater than the moment of inertia, 1 with respect to the slowrotation axis, Z. The reason for this difference is evident from theforegoing equation because by making 1,, greater than I, the denominatorof the equation becomes significantly larger than the numerator and theresulting sin 8,, is very small, i.e., less than 1. This satisfies therequirement that the angle, B between the fast rotation axis Z and thehorizontal gimbal axis B, must be small to achieve stable operation insteady state conditions. Further, as is well known in the gyroscopicart, stable operation is evident when an equilibrium condition ispresent, and an equilibrium condition is present when kinetic energy isa maximum. To determine if maximum kinetic energy is present, theforegoing equation maybe expressed in terms of the derivative of kineticenergy with respect to the sin 8,, and equating the expression obtainedto zero. Therefore:

If the second derivative is obtained and is negative, then the kineticenergy will be a maximum; if it is positive, then the kinetic energywill be a minimum. Therefore:

The second derivative will be positive when I, is greater than 1,,indicating an unstable condition. However, in the subject device theinertial element 15 is designed so that 1,, is greater than 1,,therefore, kinetic energy is a maximum, equilibrium is present and thesteady state condition will provide stable operation.

A more detailed description of the operation of the multiple rotationgyroscope is presented in copending U.S. application Ser. No. 392,676.

Referring again to FIG. 1, the 2 of freedom multiple rotation gyroscope10 constructed in accordance with the present invention has a case 11 inwhich a gimbal 12 is rotatably supported and may be spun by drive motor13 at a fast rotation speed with respect to the case 11 about the Aaxis. The gimbal v12 may be rotatable with respect to the case 11 byspaced ball bearings 14 or by other bearing means knownin the art. Theinertial element 15 is hydrodynamically supported by a fluid 16 withinthe cavity 23 of the gimbal 12. The fluid 16 may be a liquid consistingof a fluorocarbon such as FC75. The ferro-magnetic poles 17 S arid N ofa pickoff-torquer 18 and the magnetic poles 19 N and S of the inertialelement 15 tend to hold the inertial element 15 in synchronism with thegimbal 12 as the inertial element 15 spins about the V axis. Eddycurrent torque motors 20 rotate the inertial element 15 at a slowrotation speed with respect to the gimbal 12 about the Z axis.

The inertial element 15 may comprise a high density material such as adumbbell-shaped magnet 21 fabricated of platinum cobalt disposed withina hollow low density metal sphere 22, the latter being fabricated ofberyllium, for example.

The description of synchronous loading as applied to the inertialelement 15 will now be described with reference to'FIG. 1. In thisdescription the axes of fast and slow rotation will be referred to asthe A and B axes, respectively, it being understood from the foregoingremarks that the V and Z axes are substantially aligned to the A and Baxes except for the slight angular displacement B Assume the gyroscopeis turned off, the temperature is relatively low and the inertialelement 15 is floating at the top of the cavity 23 within the gimbal 12.When the gyroscope is turned on, the inertial element'lS will becomecentered within the cavity 23 because the flotation liquid at a lowtemperature is more dense than the inertial element 15 and the resultingcentrifugal forces act upon the inertial element 15, cause it to becomecentered in the plane normal to the A, and centered in the cavity alongaxis A due to the hydrodynamic lift generated by the inertial element(15) rotating about axis B. As the temperature increases to exactly thatrequired from neutral buoyancy, the inertial element 15 will remaincentered, if the synchronous forces are balanced. Synchronous forces areforces acting on the inertial element 15 which spin in synchronism withthe inertial element 15 and the gimbal 12 as they rotate about the Aaxis thereby causing the inertial element 15 to translate along the Baxis toward the wall of the cavity 23 in the gimbal 12. Nonsynchronousforces are forces which act on the inertial element 15 tending todecenter it, but are not in synchronism with the inertial element 15 andgimbal 12 as they rotate about the A axis. Non-synchronous forces areresisted by the increased hydrodynamic stiffness produced by the dynamicaction of the inertial element 15 acting in combination with theflotation fluid 16 and the wall of the cavity 23 in the gimbal 12. As aresult, any translation of the inertial element 15 along the A axis oran axis perpendicular to the A and B axes would result in a restoringforce tending to center the inertial element 15.

The pick-off torquer ferro-magnetic poles 17 S and N and the rotormagnetic poles 19 S and N create magnetic forces which result insynchronous forces being applied to the inertial element 15. Since it isextremely difficult to maintain the magnetic force due to the magneticpoles 19 N and 17 S exactly equal to the magnetic force due to themagnetic poles 19 S and 17 N, an unbalance can easily occur.

Even when the inertial element is positioned exactly in the centerbetween the magnetic poles 17 S and 17 N and the net force difference iszero, once any dislocation of the inertial element 15 from exact centertakes place, an unbalance will occur and the resulting forces will tendto decenter the inertial element 15. For example, a transient change inthe buoyancy of the flotation fluid due to temperature variation cancause an unbalance in the zero net force difference between the magneticpoles 17 S and 17 N. The inertial element 15 in response to thisunbalanced condition will translate along the B axis towards magneticpoles 17 N or 17 S. Since there is no restraining force along the B axisto counteract the unbalance in the magnetic forces, the inertial element15 will continue to be displaced until it comes in contact with the wallof the cavity 23 in the gimbal 12. As a consequence, the inertialelement 15 will no longer produce relative motion between the inertialelement 15 and the gimbal 12 thereby causing the gyroscope to beinoperative.

This deficiency in the hydrodynamically supported inertial element 15 isovercome in the present invention by additional bearing surfaces whichproduce sufficient hydrodynamic stiffness to provide a restraining forceto synchronous loads applied parallel to the B axis. The specificpurpose of the additional bearing surfaces is to form a built-in wedgeaction. There are many geometric shapes and forms available as possiblechoices for these surface features including step grooves, taperedwedges, curved ridges, herringbone, and spiral grooves. Present state ofthe art practical fabrication considerations narrows the possibilitiesto either step or spiral grooves and it has been theoreticallyestablished that the spiral groove bearing excels by a factor of 2:1 to4:1 over the step bearing. Therefore, in a specific embodiment of thepresent invention spiral grooves were profiled on the walls of thespherical cavity 23 within the gimbal 12 as shown in FIG. 2. Eightspiral grooves 25 having a spiral angle of 65, an outside diameter of13/16 inches and an inside diameter of h inch were eroded in thespherical surface in the vicinity of the poles of the B axis. Othertechniques may be used equally well to effect these grooves includingetching and casting. The spherical diameter of the inertial element 15was 1.250 inches and the radial clearance between the surface of theinertial element 15 and the wall of the cavity was 0.0011 inch. Theratio of the radial clearance to the groove depth was 1:1. For optimumperformance the radial clearance should be of the same order ofmagnitude as the groove depth.

In a multiple rotation gyroscope incorporating the additional bearingsurfaces, assume an unbalance in the zero net force difference betweenthe magnetic poles 17 S and 17 N occurs, and the inertial element 15translates toward the magnetic pole 17 S. Since the surface featuresprovide built-in wedge action through the action of the surfaces 26 ofthe spiral grooves 25 acting on the flotation fluid 16, the restoringforce will increase as the bearing gap decreases. The restoring forceproduced between the inertial element 15 and the wall of the cavity 23within the gimbal 12 in the region of the magnetic pole 17 S willgreatly increase. At the same time in the region of the magnetic pole 17N the restoring force will decrease because the gap has increased.Therefore, the inertial element 15 responding to this difference inforce will translate back along the B axis toward the center of thecavity 23. Any further displacement along the B axis will result in asimilar increase in force acting on the surface of the inertial element15 in a direction opposite to the displacement, thereby maintaining theinertial element 15 centered within the cavity of the gimbal 12.

An alternative embodiment of the present invention is shown in FIG. 3.In this embodiment the additional bearing surfaces are provided byspiral grooves 25 profiled on the surface of the inertial element 15 inthe region of the horizontal axis B.

While the invention has been described in its preferred embodiment, itis to be understood that the words which have been used are words ofdescription rather than limitation and that changes may be made withinthe purview of the appended claims without departing from the true scopeand spirit of the invention in its broader aspects.

Iclaim: 1. a gyroscopic apparatus comprising an inertial element havingfirst and second mutually perpendicular axes of inertial symmetry, saidinertial element simultaneously rotating about said first and secondaxes and having a moment of inertia and angular velocity component aboutsaid first axis which is greater than its moment of inertia and angularvelocity component about said second axis, gimbal means for rotatingabout said first axis in synchronism with said inertial elementincluding an internal cavity enclosing said inertial element,

first and second fluid bearing means disposed between said gimbal meansand said inertial element for hydrodynamically suspending said inertialelement in a centered position along said first and second axes withinsaid cavity,

means mounted in said gimbal means for providing synchronous forceswhich act on said inertial element and spin in synchronism with saidinertial element and said gimbal means as they rotate about said firstaxis, and

third fluid bearing means disposed between said gimbal means and saidinertial element for providing restoring forces which compensateunbalanced conditions in said synchronous forces decenter said inertialelement along said second axis whereby said restoring forces translatesaid inertial element along said second axis to restore it to a centeredposition within said cavity.

2. A gyroscopic apparatus as defined in claim 1 in which said first andsecond fluid bearing means include a relatively viscous fluid disposedbetween the internal surfaces of said cavity and the external surfacesof said inertial element which co-acts with these surfaces in responseto said simultaneous rotation of said inertial element about first andsecond axes, and

said third fluid bearing means includes additional surfaces between saidinternal surfaces of said cavity and said external surfaces of saidinertial that v ,5. A gyroscopic apparatus as defined in claim 2 inwhich said third fluid bearing means includes spiral grooves profiled onthe surface of said inertial element in the region of the poles of saidsecond axis of rotation.

6. A gyroscopic apparatus as defined in claim 2 in which said thirdfluid bearing means. includes spiral grooves profiled on the walls ofsaid cavity of said gimbal in the region of the poles of said secondaxis of rotation.

1. A GYROSCOPIC APPARATUS COMPRISING AN INERTIAL ELEMENT HAVING FIRSTAND SECOND MUTUALLY PERPENDICULAR AXES OF INERTIAL SYMMETRY, SAIDINERTIAL ELEMENT SIMULTANEOUSLY ROTATING ABOUT SAID FIRST AND SECONDAXES AND HAVING A MOMENT OF INERTIA AND ANGULAR VELOCITY COMPONENT ABOUTSAID FIRST AXIS WHICH IS GREATER THAN ITS MOMENT OF INERTIA AND ANGULARVELOCITY COMPONENT ABOUT SAID SECOND AXIS, GIMBAL MEANS FOR ROTATINGABOUT SAID FIRST AXIS IN SYNCHRONISM WITH SAID INERTIAL ELEMENTINCLUDING AN INTERNAL CAVITY ENCLOSING SAID INERTIAL ELEMENT, FIRST ANDSECOND FLUID BEARING MEANS DISPOSED BETWEEN SAID GIMBAL MEANS AND SAIDINERTIAL ELEMENT FOR HYDRODYNAMICALLY SUSPENDING SAID INERTIAL ELEMENTIN A CENTERED POSITION ALONG SAID FIRST AND SECOND AXES WITHIN SAIDCAVITY, MEANS MOUNTED IN SAID GIMBAL MEANS FOR PROVIDING SYNCHRONOUSFORCES WHICH ACT ON SAID INERTIAL ELEMENT AND SPIN IN SYNCHRONISM WITHSAID INERTIAL ELEMENT AND SAID GIMBAL MEANS AS THEY ROTATE ABOUT SAIDFIRST AXIS, AND THIRD FLUID BEARING MEANS DISPOSED BETWEEN SAID GIMBALMEANS AND SAID INERTIAL ELEMENT FOR PROVIDING RESTORING FORCES WHICHCOMPENSATE UNBALANCED CONDITIONS IN SAID SYNCHRONOUS FORCES THATDECENTER SAID INERTIAL ELEMENT ALONG SAID SECOND AXIS WHEREBY SAIDRESTORING FORCES TRANSLATE SAID INERTIAL ELEMENT ALONG SAID SECOND AXISTO RESTORE IT TO A CENTERED POSITION WITHIN SAID CAVITY.
 2. A gyroscopicapparatus as defined in claim 1 in which said first and second fluidbearing means include a relatively viscous fluid disposed between theinternal surfaces of said cavity and the external surfaces of saidinertial element which co-acts with these surfaces in response to saidsimultaneous rotation of said inertial element about first and secondaxes, and said third fluid bearing means includes additional surfacesbetween said internal surfaces of said cavity and said external surfacesof said inertial element which co-act with said relatively viscous fluidto provide said restoring forces.
 3. A gyroscopic apparatus as definedin claim 2 in which said third fluid bearing means includes surfacefeatures profiled on the surface of said inertial element in the regionof the poles of said second axis of rotation.
 4. A gyroscopic apparatusas defined in claim 2 in which said third fluid bearing means includessurface features profiled on the walls of said cavity of said gimbal inthe region of the poles of said second axis of rotation.
 5. A gyroscopicapparatus as defined in claim 2 in which said third fluid bearing meansincludes spiral grooves profiled on the surface of said inertial elementin the region of the poles of said second axis of rotation.
 6. Agyroscopic apparatus as defined in claim 2 in which said third fluidbearing means includes spiral grooves profiled on the walls of saidcavity of said gimbal in the region of the poles of said second axis ofrotation.